Managing communication interference in leadless dual-chamber pacing systems and other IMD systems

ABSTRACT

Embodiments described herein relate to implantable medical devices (IMDs) and methods for use therewith. Such a method includes, during each of a plurality of message alert periods during which a communication capability of the IMD is enabled, determining whether a valid message is detected. In response to determining that no valid message was detected during a message alert period, the communication capability of the IMD is temporarily disable for a disable period. A length of the disable period may be increased in response to no valid message being detected during two consecutive message alert periods. A length of the disable period may be dependent on an operational mode of the IMD, such that the length of the disable period differs for different operational modes. The IMD may also enter a noise state, and remain in the noise state until the IMD receives a specified number of valid messages.

PRIORITY CLAIM

This application is a continuation U.S. patent application Ser. No.16/819,690, filed Mar. 16, 2020, which issued as U.S. Pat. No.11,097,112, which is a continuation of U.S. patent application Ser. No.15/976,788, filed May 10, 2018, which issued as U.S. Pat. No.10,632,315. Priority is claimed to each of the above applications, andeach of the above applications is incorporated herein by reference inits entirety.

RELATED APPLICATIONS

This application is related to the following commonly assigned patentapplications, each of which is incorporated herein by reference: U.S.patent application Ser. No. 15/413,820, titled MITIGATING EXCESSIVEWAKEUPS IN LEADLESS DUAL-CHAMBER PACING SYSTEMS AND OTHER IMD SYSTEMSFIELD OF TECHNOLOGY, filed Jan. 24, 2017; U.S. patent application Ser.No. 15/423,404, titled MITIGATING FALSE MESSAGING IN LEADLESSDUAL-CHAMBER PACING SYSTEMS AND OTHER IMD SYSTEMS, filed Feb. 2, 2017;and U.S. patent application Ser. No. 15/423,409, titled MITIGATING FALSEMESSAGING IN LEADLESS DUAL-CHAMBER PACING SYSTEMS AND OTHER IMD SYSTEMS,filed Feb. 2, 2017.

FIELD OF TECHNOLOGY

Embodiments described herein generally relate to methods and systems forcommunication between implantable medical devices, or communicatingbetween a non-implantable device and an implantable medical device.

BACKGROUND

The longevity of an implantable medical device (IMD) that is powered bya battery is dependent upon how much power is consumed by electronics ofthe device. Such electronics can be used, e.g., for pacing or deliveringother types of stimulation, sensing or otherwise collecting information,as well as for communicating within another implantable device or anon-implantable device. Accordingly, power may be consumed when pacingor delivering other types of stimulation, collecting information, aswell as when communicating. It would be beneficial to reduce powerconsumption in order to increase the longevity of an IMD.

SUMMARY

Embodiments of the present technology relate to implantable medicaldevices (IMDs) and methods for use therewith. A method according to anembodiment of the present technology includes enabling a communicationcapability of an IMD during a message alert period, and monitoring for amessage while the communication capability of the IMD is enabled duringthe message alert period. In response to receiving a message during themessage alert period, there is a determination whether the message isvalid or invalid. In response to determining that the message isinvalid, the message is ignored and an invalid message count isincremented. Monitoring for a further message during the message alertperiod occurs, when the invalid message count has not yet reached acorresponding invalid message count threshold. The communicationcapability of the IMD is disabled for a disable period, when the invalidmessage count reaches the corresponding invalid message count threshold.In response to determining that a received message is valid, the IMDacts upon information included in the message.

In accordance with certain embodiments, the communication capability ofthe IMD, which is enabled during the message alert period, and which isdisabled when the invalid message count reaches the correspondinginvalid message count threshold, can be: a receiver of the IMD itself,an input to the receiver of the IMD, and/or an output from the receiverof the IMD.

In accordance with certain embodiments, the IMD includes a firstreceiver and a second receiver, wherein the first receiver is used toselectively wakeup the second receiver, and wherein the second receiverwhen awake consumes more power than the first receiver. The method canbe used to reduce how often the first receiver wakes up the secondreceiver and thereby reduces how much power is consumed by the secondreceiver. In such an embodiment, the communication capability of theIMD, which is enabled during the message alert period, and which isdisabled when the invalid message count reaches the correspondinginvalid message count threshold, can be: the first receiver itself, aninput to the first receiver, and/or an output from the first receiver.

In accordance with certain embodiments, the disable period during whichthe communication capability of the IMD is disabled, in response to theinvalid message count reaching the corresponding invalid message countthreshold, comprises a specified number of cardiac cycles, or aspecified number of units of time.

In accordance with certain embodiments, the invalid message countthreshold is specified in dependence on whether a valid message wasdetected during an immediately preceding message alert period. Forexample, the invalid message count threshold can be reduced if a validmessage was not detected during an immediately preceding message alertperiod, compared to if a valid message was detected during theimmediately preceding message alert period.

In accordance with certain embodiments, a length of the disable periodduring which the communication capability of the IMD is disabled, inresponse to the invalid message count reaching the corresponding invalidmessage count threshold, depends on which one of a plurality ofoperational modes the IMD is set to, and thus, operating in. Exemplaryoperational modes that an IMD can be set to include, but are not limitedto, a normal operational mode, a magnetic resonance imaging (MRI) readyoperational mode, or a radio frequency (RF) ablation ready operationalmode.

In accordance with certain embodiments, the invalid message countthreshold depends on which one of a plurality of operational modes theIMD is set to, and thus, operating in.

In accordance with certain embodiments, an amount by which the invalidmessage count is incremented, in response to determining that a messagereceived during a message alert period is invalid, is greater if a validmessage was not detected during an immediately preceding message alertperiod, compared to if a valid message was detected during theimmediately preceding message alert period.

In accordance with certain embodiments, when the communicationcapability of the IMD is disabled the IMD enters a noise state duringwhich the IMD operates in a safe pacing mode, and wherein once the IMDhas entered the noise state the IMD does not exit the noise state untila valid message is received in a specified number of consecutive messagealert periods.

An implantable medical device (IMD) according certain embodiments of thepresent technology includes a receiver configured to monitor for amessage transmitted by another IMD or a non-implanted device. The IMDalso includes a processor or controller configured to control or trackmessage alert periods and configured to enable a communicationcapability associated with the receiver during each message alertperiod. The processor or controller can also be configured to performthe following in response to the receiver receiving a message during amessage alert period: determine whether the message is valid or invalid;ignore the message and increment an invalid message count, in responseto determining that the message is invalid; keep the communicationcapability associated with the receiver enabled during the message alertperiod, when the invalid message count has not yet reached acorresponding invalid message count threshold; and disable thecommunication capability associated with the receiver for a disableperiod, when the invalid message count reaches the corresponding invalidmessage count threshold. Additionally, the processor or controller canbe configured to act upon information included in a received message, inresponse to determining that the received message is valid.

In accordance with certain embodiments, the communication capabilityassociated with the receiver, which is enabled during the message alertperiod, and which is disabled when the invalid message count reaches thecorresponding invalid message count threshold, comprises at least one ofan input to the receiver or an output from the receiver.

In accordance with certain embodiments, the receiver that is configuredto monitor for a message is a first receiver, and the IMD also includesa second receiver that is selectively awakened by the first receiver,wherein the second receiver when awake consumes more power than thefirst receiver. In such an embodiment, the communication capabilityassociated with the receiver, which is enabled during the message alertperiod, and which is disabled when the invalid message count reaches thecorresponding invalid message count threshold, can be an input to thefirst receiver and/or an output from the first receiver.

In accordance with certain embodiments, the disable period during whichthe communication capability associated with the receiver is disabled,in response to the invalid message count reaching the correspondinginvalid message count threshold, comprises a specified number of cardiaccycles or a specified number of units of time.

In accordance with certain embodiments, the processor is configured toreduce the invalid message count threshold if a valid message was notdetected during an immediately preceding message alert period, comparedto if a valid message was detected during the immediately precedingmessage alert period.

In accordance with certain embodiments, the IMD is capable of operatingin a plurality of operation modes, and a length of the disable periodduring which the communication capability associated with the receiveris disabled, in response to the invalid message count reaching thecorresponding invalid message count threshold, depends on which one ofthe plurality of operational modes the IMD is set to, and thus,operating in.

In accordance with certain embodiments, when the communicationcapability associated with the receiver is disabled the IMD enters anoise state during which the IMD operates in a safe pacing mode, andwherein once the IMD has entered the noise state the IMD does not exitthe noise state until a valid message is received in a specified numberof consecutive message alert periods.

Methods according to certain embodiments of the present technology arefor use by an IMD including a first receiver and a second receiver,wherein the first receiver is used to selectively wakeup the secondreceiver, and wherein the second receiver when awake consumes more powerthan the first receiver. Such methods can reduce how often the firstreceiver wakes up the second receiver and thereby reduce how much poweris consumed by the second receiver. Such a method can include enablingat least one of the first receiver, an input to the first receiver, oran output from the first receiver during a message alert period, andmonitoring for a message during the message alert period. Such a methodcan also include, in response to receiving a message using the firstreceiver during the message alert period, waking up the second receiverand using the second receiver to determine whether the message is validor invalid. In response to determining that the message is invalid, themessage is ignored and an invalid message count is incremented.Monitoring for a further message occurs during the message alert period,when the invalid message count has not yet reached a correspondinginvalid message count threshold. At least one of the first receiver, aninput to the first receiver, or an output from the first receiver isdisable for a disable period, when the invalid message count reaches thecorresponding invalid message count threshold. In response to a validmessage being received, information included in the message is actedupon.

This summary is not intended to be a complete description of theembodiments of the present technology. Other features and advantages ofthe embodiments of the present technology will appear from the followingdescription in which the preferred embodiments have been set forth indetail, in conjunction with the accompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present technology relating to both structure andmethod of operation may best be understood by referring to the followingdescription and accompanying drawings, in which similar referencecharacters denote similar elements throughout the several views:

FIG. 1 illustrates a system formed in accordance with certainembodiments herein as implanted in a heart.

FIG. 2 is a block diagram of a single leadless pacemaker (LP) inaccordance with certain embodiments herein.

FIG. 3 illustrates a LP in accordance with certain embodiments herein.

FIG. 4 is a timing diagram demonstrating one embodiment of implant toimplant (i2i) communication for a paced event.

FIG. 5 is a timing diagram demonstrating one embodiment of i2icommunication for a sensed event.

FIGS. 6A and 6B are high level flow diagrams that are used to summarizemethods according to various embodiments of the present technology thatare for use by an IMD, such as an LP, and which methods can be used, forexample, to reduce how often a first receiver of a device wakes up asecond receiver of the device and thereby reduces power consumed by thedevice, but are not limited thereto.

FIG. 7 shows a block diagram of one embodiment of an LP that isimplanted into the patient as part of the implantable cardiac system inaccordance with certain embodiments herein.

DETAILED DESCRIPTION

In some embodiments of an illustrative cardiac pacing system, pacing andsensing operations of multiple medical devices, which may include one ormore leadless cardiac pacemakers, an implantablecardioverter-defibrillator (ICD), such as a subcutaneous-ICD, and/or aprogrammer reliably and safely coordinate pacing and/or sensingoperations.

FIG. 1 illustrates a system 100 formed in accordance with certainembodiments herein as implanted in a heart 101. The system 100 comprisestwo or more leadless pacemakers (LPs) 102 and 104 located in differentchambers of the heart. LP 102 is located in a right atrium, while LP 104is located in a right ventricle. LPs 102 and 104 communicate with oneanother to inform one another of various local physiologic activities,such as local intrinsic events, local paced events and the like. LPs 102and 104 may be constructed in a similar manner, but operate differentlybased upon which chamber LP 102 or 104 is located.

In some embodiments, LPs 102 and 104 communicate with one another, withan ICD 106, and with an external device (programmer) 109 throughwireless transceivers, communication coils and antenna, and/or byconductive communication through the same electrodes as used for sensingand/or delivery of pacing therapy. When conductive communication ismaintained through the same electrodes as used for pacing, the system100 may omit an antenna or telemetry coil in one or more of LPs 102 and104.

In some embodiments, one or more leadless cardiac pacemakers 102 and 104can be co-implanted with the implantable cardioverter-defibrillator(ICD) 106. Each leadless cardiac pacemaker 102, 104 uses two or moreelectrodes located within, on, or within a few centimeters of thehousing of the pacemaker, for pacing and sensing at the cardiac chamber,for bidirectional communication with one another, with the programmer109, and the ICD 106.

In accordance with certain embodiments, methods are provided forcoordinating operation between leadless pacemakers (LPs) located indifferent chambers of the heart. The methods configure a local LP toreceive communications from a remote LP through conductivecommunication.

While the methods and systems described herein include examplesprimarily in the context of LPs, it is understood that the methods andsystems herein may be utilized with various other external and implanteddevices. By way of example, the methods and systems may coordinateoperation between various implantable medical devices (IMDs) implantedin a human, not just LPs. The methods and systems comprise configuring afirst IMD to receive communications from at least a second IMD throughconductive communication over at least a first channel. It should alsobe understood that the methods and systems may coordinate operationbetween multiple IMDs, and are not limited to coordinate operationbetween just a first and second IMD. The methods and systems may also beused to coordinate operation of two or more IMDs implanted within thesame chamber that may be the same type of IMD or may be different typesof IMDs. The methods and systems may also be used to coordinateoperation of two or more IMDs in a system comprising at least one IMDimplanted but not within a heart chamber, e.g., epicardially,transmurally, intravascularly (e.g., coronary sinus), subcutaneously(e.g., S-ICD), etc.

Referring to FIG. 2 , a pictorial diagram shows an embodiment forportions of the electronics within LP 102, 104 configured to provideconducted communication through the sensing/pacing electrode. One ormore of LPs 102 and 104 comprise at least two leadless electrodes 108configured for delivering cardiac pacing pulses, sensing evoked and/ornatural cardiac electrical signals, and uni-directional orbi-directional communication.

LP 102, 104 includes a transmitter 118 and first and second receivers120 and 122 that collectively define separate first and secondcommunication channels 105 and 107 (FIG. 1 ), (among other things)between LPs 102 and 104. Although first and second receivers 120 and 122are depicted, in other embodiments, LP 102, 104 may only include firstreceiver 120, or may include additional receivers other than first andsecond receivers 120 and 122. LP 102, 104 may also include one or moretransmitters in addition to transmitter 118. In certain embodiments, LPs102 and 104 may communicate over more than just first and secondcommunication channels 105 and 107. In certain embodiments, LPs 102 and104 may communicate over one common communication channel 105. Thetransmitter 118 and receiver(s) 120, 122 may each utilize a separateantenna or may utilize a common antenna 128. Optionally, LPs 102 and 104communicate conductively over a common physical channel via the sameelectrodes 108 that are also used to deliver pacing pulses. Usage of theelectrodes 108 for communication enables the one or more leadlesscardiac pacemakers 102 and 104 for antenna-less and telemetry coil-lesscommunication.

When LP 102, 104 senses an intrinsic event or delivers a paced event,the corresponding LP 102, 104 transmits an implant event message to theother LP 102, 104. For example, when an atrial LP 102 senses/paces anatrial event, the atrial LP 102 transmits an implant event messageincluding an event marker indicative of a nature of the event (e.g.,intrinsic/sensed atrial event, paced atrial event). When a ventricularLP 104 senses/paces a ventricular event, the ventricular LP 104transmits an implant event message including an event marker indicativeof a nature of the event (e.g., intrinsic/sensed ventricular event,paced ventricular event). In certain embodiments, LP 102, 104 transmitsan implant event message to the other LP 102, 104 preceding the actualpace pulse so that the remote LP can blank its sense inputs inanticipation of that remote pace pulse (to prevent inappropriatecrosstalk sensing).

The implant event messages may be formatted in various manners. As oneexample, each event message may include a leading trigger pulse (alsoreferred to as an LP wakeup notice or wakeup pulse) followed by an eventmarker. The notice trigger pulse is transmitted over a first channel(e.g., with a pulse duration of approximately 10 μs to approximately 1ms and/or within a fundamental frequency range of approximately 1 kHz toapproximately 100 kHz). The notice trigger pulse indicates that an eventmarker is about to be transmitted over a second channel (e.g., within ahigher frequency range). The event marker can then be transmitted overthe second channel.

The event markers may include data indicative of one or more events(e.g., a sensed intrinsic atrial activation for an atrial located LP, asensed intrinsic ventricular activation for a ventricular located LP).The event markers may include different markers for intrinsic and pacedevents. The event markers may also indicate start or end times fortimers (e.g., an AV interval, a blanking interval, etc.). Optionally,the implant event message may include a message segment that includesadditional/secondary information.

Optionally, the LP (or other IMD) that receives any implant to implant(i2i) communication from another LP (or other IMD) or from an externaldevice may transmit a receive acknowledgement indicating that thereceiving LP/IMD received the i2i communication, etc.

The event messages enable the LPs 102, 104 to deliver synchronizedtherapy and additional supportive features (e.g., measurements, etc.).To maintain synchronous therapy, each of the LPs 102 and 104 is madeaware (through the event messages) when an event occurs in the chambercontaining the other LP 102, 104. Some embodiments described hereinprovide efficient and reliable processes to maintain synchronizationbetween LPs 102 and 104 without maintaining continuous communicationbetween LPs 102 and 104. In accordance with certain embodiments herein,the transmitter(s) 118 and receiver(s) 120, 122 utilize low power eventmessages/signaling between multiple LPs 102 and 104. The low power eventmessages/signaling may be maintained between LPs 102 and 104synchronously or asynchronously.

For synchronous event signaling, LPs 102 and 104 maintainsynchronization and regularly communicate at a specific interval.Synchronous event signaling allows the transmitter and receivers in eachLP 102,104 to use limited (or minimal) power as each LP 102, 104 is onlypowered for a small fraction of the time in connection with transmissionand reception. For example, LP 102, 104 may transmit/receive (Tx/Rx)communications in time slots having duration of 10-20 μs, where theTx/Rx time slots occur periodically (e.g., every 10-20 ms). In theforegoing example, a receiver 120, 122 that is active/ON (also referredto as awake) for select receive time slots, that are spaced apartseveral milliseconds, may draw an amount of current that is severaltimes less (e.g., 1000× less) than a current draw of a receiver that is“always on” (always awake).

LPs 102 and 104 may lose synchronization, even in a synchronous eventsignaling scheme. As explained herein, features may be included in LPs102 and 104 to maintain device synchronization, and when synchronizationis lost, LPs 102 and 104 undergo operations to recover synchronization.Also, synchronous event messages/signaling may introduce a delay betweentransmissions which causes a reaction lag at the receiving LP 102, 104.Accordingly, features may be implemented to account for the reactionlag.

During asynchronous event signaling, LPs 102 and 104 do not maintaincommunication synchronization. During asynchronous event signaling, oneor more of receivers 120 and 122 of LPs 102 and 104 may be “always on”(always awake) to search for incoming transmissions. However,maintaining LP receivers 120, 122 in an “always on” (always awake) statepresents challenges as the received signal level often is low due tohigh channel attenuation caused by the patient's anatomy. Further,maintaining the receivers awake will deplete the battery 114 morequickly than may be desirable.

The asynchronous event signaling methods avoid risks associated withlosing synchronization between devices. However, the asynchronous eventsignaling methods utilize additional receiver current betweentransmissions. For purposes of illustration only, a non-limiting exampleis described hereafter. For example, the channel attenuation may beestimated to have a gain of 1/500 to 1/10000. A gain factor may be1/1000th. Transmit current is a design factor in addition to receivercurrent. As an example, the system may allocate one-half of the implantcommunication current budget to the transmitter (e.g., 0.5 μA for eachtransmitter). When LP 102, 104 maintains a transmitter in a continuouson-state and the electrode load is 500 ohms, a transmitted voltage maybe 0.250 mV. When an event signal is transmitted at 0.250 mV, the eventsignal is attenuated as it propagates and would appear at LP 102, 104receiver as an amplitude of approximately 0.25 μV. The receivers 120 and122 utilize a synchronization threshold to differentiate incomingcommunication signals from noise. As an example, the synchronizationthreshold may be 0.5 μV (or more generally 0.25 μV to 5 μV), which wouldcause LP 102, 104 receiver to reject an incoming communication signalthat exhibits a receive voltage below 0.5 μV.

To overcome the foregoing receive power limit, a pulsed transmissionscheme may be utilized in which communication transmissions occurcorrelated with an event. By way of example, the pulsed transmissionscheme may be simplified such that each transmission constitutes asingle pulse of a select amplitude and width.

When LP transmitter 118 transmits event signals over a conductivecommunication channel that has an electrode load of 500 ohm using a 1 mspulse width at 2.5V at a rate of 60 bpm, LP transmitter 118 will draw4.4 μA for transmit current. When LP transmitter 118 transmits eventsignals at 2.5V using a 2 μs pulse width, transmitter 118 only draws 10nA to transmit event messages at a rate of 60 bpm. In order to sense anevent message (transmitted with the foregoing parameters), receivers 120and 122 may utilize 50 μA. In accordance with certain embodimentsherein, the pulse widths and other transmit/receive parameters may beadjusted to achieve a desired total (summed) current demand from bothtransmitter 118 and receivers 120 and 122. The transmitter currentdecreases nearly linearly with narrowing bandwidth (pulse width), whilea relation between receiver current and bandwidth is non-linear.

In accordance with certain embodiments herein, LPs 102 and 104 mayutilize multi-stage receivers that implement a staged receiver wakeupscheme in order to improve reliability yet remain power efficient. Eachof LPs 102 and 104 may include first and second receivers 120 and 122that operate with different first and second activation protocols anddifferent first and second receive channels. For example, first receiver120 may be assigned a first activation protocol that is “always on”(also referred to as always awake) and that listens over a first receivechannel that has a lower fundamental frequency range/pulse duration(e.g., 1 kHz to 100 kHz/10 μs to approximately 1 ms) as compared to thefundamental frequency range (e.g., greater than 100 kHz/less than 10 μsper pulse) assigned to the second receive channel. First receiver 120may maintain the first channel active (awake) for at least a portion ofa time when the second channel is inactive (asleep) to listen for eventmessages from a remote LP. The controller or processor determineswhether the incoming signal received over the first channel correspondsto an LP wakeup notice. The second receiver 122 may be assigned a secondactivation protocol that is a triggered protocol, in which the secondreceiver 122 becomes active (awake) in response to detection of triggerevents over the first receive channel (e.g., when the incoming signalcorresponds to the LP wakeup notice, activating the second channel atthe local LP).

The marker message may represent a signature indicative of an eventqualification to qualify a valid event marker pulse. The eventqualification messages distinguish a message from spurious noise andavoid mistaking other signals as event messages having implant markers.The event message may be repeated to allow the LP receiver 120 multiplechances to “catch” the event qualification. Additionally oralternatively, the Tx and Rx LP 102, 104 may implement a handshakingprotocol in which the Tx and Rx LP 102, 104 exchange additionalinformation, such as to allow a response to follow the marker. Theexchange of additional information may be limited or avoided in certaininstances as the exchange draws additional power when sending andreceiving the information. Optionally, the event message may beconfigured with additional content to provide a more robust eventmarker.

Transmitter 118 may be configured to transmit the event messages in amanner that does not inadvertently capture the heart in the chamberwhere LP 102, 104 is located, such as when the associated chamber is notin a refractory state. In addition, a LP 102, 104 that receives an eventmessage may enter an “event refractory” state (or event blanking state)following receipt of the event message. The event refractory/blankingstate may be set to extend for a determined period of time after receiptof an event message in order to avoid the receiving LP 102, 104 frominadvertently sensing another signal as an event message that mightotherwise cause retriggering. For example, the receiving LP 102, 104 maydetect a measurement pulse from another LP 102, 104 or programmer 109.

In accordance with certain embodiments herein, programmer 109 maycommunicate over a programmer-to-LP channel, with LP 102, 104 utilizingthe same communication scheme. The external programmer may listen to theevent message transmitted between LP 102, 104 and synchronize programmerto implant communication such that programmer 109 does not transmitcommunication signals 113 until after an implant to implant messagingsequence is completed.

In accordance with certain embodiments, LP 102, 104 may combine transmitoperations with therapy. The transmit event marker may be configured tohave similar characteristics in amplitude and pulse width to a pacingpulse and LP 102, 104 may use the energy in the event messages to helpcapture the heart. For example, a pacing pulse may normally be deliveredwith pacing parameters of 2.5V amplitude, 500 ohm impedance, 60 bpmpacing rate, 0.4 ms pulse width. The foregoing pacing parameterscorrespond to a current draw of about 1.9 μA. The same LP 102, 104 mayimplement an event message utilizing event signaling parameters foramplitude, pulse width, pulse rate, etc. that correspond to a currentdraw of approximately 0.5 μA for transmit.

LP 102, 104 may combine the event message transmissions with pacingpulses. For example, LP 102, 104 may use a 50 μs wakeup transmit pulsehaving an amplitude of 2.5V which would draw 250 nC (nano Coulombs) foran electrode load of 500 ohm. The pulses of the transmit event messagemay be followed by an event message encoded with a sequence of shortduration pulses (for example 16, 2 μs on/off bits) which would draw anadditional 80 nC. The event message pulse would then be followed by theremaining pulse width needed to reach an equivalent charge of a nominal0.4 ms pace pulse. In this case, the current necessary to transmit themarker is essentially free as it was used to achieve the necessary pacecapture anyhow. With this method, the savings in transmit current couldbe budgeted for the receiver or would allow for additional longevity.

When LP 102, 104 senses an intrinsic event, the transmitter sends aqualitatively similar event pulse sequence (but indicative of a sensedevent) without adding the pace pulse remainder. As LP 102, 104 longevitycalculations are designed based on the assumption that LP 102, 104 willdeliver pacing therapy 100% of the time, transmitting an intrinsic eventmarker to another LP 102, 104 will not impact the nominal calculated LPlongevity.

In some embodiments, LP 102, 104 may deliver pacing pulses at relativelylow amplitude. When low amplitude pacing pulses are used, the powerbudget for event messages may be modified to be a larger portion of theoverall device energy budget. As the pacing pulse amplitude is loweredcloser to amplitude of event messages, LP 102, 104 increases an extentto which LP 102, 104 uses the event messages as part of the pacingtherapy (also referred to as sharing “capture charge” and “transmitcharge”). As an example, if the nominal pacing voltage can be lowered to<1.25 V, then a “supply halving” pacing charge circuit could reduce thebattery current draw by approximately 50%. A 1.25V pace pulse would save1.5 μA of pacing current budget. With lower pulse amplitudes, LP 102,104 may use larger pulse widths.

By combining event messages and low power pacing, LP 102, 104 mayrealize additional longevity. Today longevity standards provide that thelongevity to be specified based on a therapy that utilizes 2.5Vamplitude, 0.4 ms pulses at 100% pacing. Optionally, a new standard maybe established based on pacing pulses that deliver lower amplitudeand/or shorter pacing pulses.

In an embodiment, a communication capacitor is provided in LP 102, 104.The communication capacitor may be used to transmit event signals havinghigher voltage for the event message pulses to improve communication,such as when the LPs 102 and 104 experience difficulty sensing eventmessages. The high voltage event signaling may be used for implants withhigh signal attenuation or in the case of a retry for an ARQ (automaticrepeat request) handshaking scheme.

For example, when an LP 102, 104 does not receive an event messagewithin a select time out interval, LP 102, 104 may resend an eventmessage at a higher amplitude. As another example, LP 102, 104 mayperform an event signaling auto-level search wherein the LPs send eventmessages at progressively higher amplitude until receiving confirmationthat an event message was received (or receiving a subsequent eventmessage from another LP). For example, in DDD mode when the atrial orventricular LP 102, 104 does not see an event signal from LP 102, 104 inthe other chamber before its timeout interval it could automaticallyraise the amplitude of the event message, until the LPs 102 and 104become and remain in sync. Optionally, LP 102, 104 may implement asearch hysteresis algorithm similar to those used for rate and amplitudecapture to allow the lowest safe detectible amplitude to be determined.

The LPs 102 and 104 may be programmable such as to afford flexibility inadjusting the event marker pulse width. In some embodiments, differentreceiver circuits may be provided and selected for certain pulse widths,where multiple receivers may be provided on a common ASIC, therebyallowing the user to vary the parameters in an LP after implant.

In some embodiments, the individual LP 102 can comprise a hermetichousing 110 configured for placement on or attachment to the inside oroutside of a cardiac chamber and at least two leadless electrodes 108proximal to the housing 110 and configured for bidirectionalcommunication with at least one other device 106 within or outside thebody.

FIG. 2 depicts a single LP 102 and shows the LP's functional elementssubstantially enclosed in a hermetic housing 110. The LP 102 has atleast two electrodes 108 located within, on, or near the housing 110,for delivering pacing pulses to and sensing electrical activity from themuscle of the cardiac chamber, and for bidirectional communication withat least one other device within or outside the body. Hermeticfeedthroughs 130, 131 conduct electrode signals through the housing 110.The housing 110 contains a primary battery 114 to supply power forpacing, sensing, and communication. The housing 110 also containscircuits 132 for sensing cardiac activity from the electrodes 108,circuits 134 for receiving information from at least one other devicevia the electrodes 108, and a pulse generator 116 for generating pacingpulses for delivery via the electrodes 108 and also for transmittinginformation to at least one other device via the electrodes 108. Thehousing 110 can further contain circuits for monitoring device health,for example a battery current monitor 136 and a battery voltage monitor138, and can contain circuits for controlling operations in apredetermined manner.

Additionally or alternatively, one or more leadless electrodes 108 canbe configured to communicate bidirectionally among the multiple leadlesscardiac pacemakers and/or the implanted ICD 106 to coordinate pacingpulse delivery and optionally other therapeutic or diagnostic featuresusing messages that identify an event at an individual pacemakeroriginating the message and a pacemaker receiving the message react asdirected by the message depending on the origin of the message. An LP102, 104 that receives the event message reacts as directed by the eventmessage depending on the message origin or location. In some embodimentsor conditions, the two or more leadless electrodes 108 can be configuredto communicate bidirectionally among the one or more leadless cardiacpacemakers 102 and/or the ICD 106 and transmit data including designatedcodes for events detected or created by an individual pacemaker.Individual pacemakers can be configured to issue a unique codecorresponding to an event type and a location of the sending pacemaker.

In some embodiments, an individual LP 102, 104 can be configured todeliver a pacing pulse with an event message encoded therein, with acode assigned according to pacemaker location and configured to transmita message to one or more other leadless cardiac pacemakers via the eventmessage coded pacing pulse. The pacemaker or pacemakers receiving themessage are adapted to respond to the message in a predetermined mannerdepending on type and location of the event.

Moreover, information communicated on the incoming channel can alsoinclude an event message from another leadless cardiac pacemakersignifying that the other leadless cardiac pacemaker has sensed aheartbeat or has delivered a pacing pulse, and identifies the locationof the other pacemaker. For example, LP 104 may receive and relay anevent message from LP 102 to the programmer. Similarly, informationcommunicated on the outgoing channel can also include a message toanother leadless cardiac pacemaker or pacemakers, or to the ICD, thatthe sending leadless cardiac pacemaker has sensed a heartbeat or hasdelivered a pacing pulse at the location of the sending pacemaker.

Referring again to FIGS. 1 and 2 , the cardiac pacing system 100 maycomprise an implantable cardioverter-defibrillator (ICD) 106 in additionto leadless cardiac pacemaker 102, 104 configured for implantation inelectrical contact with a cardiac chamber and for performing cardiacrhythm management functions in combination with the implantable ICD 106.The implantable ICD 106 and the one or more leadless cardiac pacemakers102, 104 configured for leadless intercommunication by informationconduction through body tissue and/or wireless transmission betweentransmitters and receivers in accordance with the discussed herein.

In a further embodiment, a cardiac pacing system 100 comprises at leastone leadless cardiac pacemaker 102, 104 configured for implantation inelectrical contact with a cardiac chamber and configured to performcardiac pacing functions in combination with the co-implantedimplantable cardioverter-defibrillator (ICD) 106. The leadless cardiacpacemaker or pacemakers 102 comprise at least two leadless electrodes108 configured for delivering cardiac pacing pulses, sensing evokedand/or natural cardiac electrical signals, and transmitting informationto the co-implanted ICD 106.

As shown in the illustrative embodiments, a leadless cardiac pacemaker102, 104 can comprise two or more leadless electrodes 108 configured fordelivering cardiac pacing pulses, sensing evoked and/or natural cardiacelectrical signals, and bidirectionally communicating with theco-implanted ICD 106.

LP 102, 104 can be configured for operation in a particular location anda particular functionality at manufacture and/or at programming by anexternal programmer. Bidirectional communication among the multipleleadless cardiac pacemakers can be arranged to communicate notificationof a sensed heartbeat or delivered pacing pulse event and encoding typeand location of the event to another implanted pacemaker or pacemakers.LP 102, 104 receiving the communication decode the information andrespond depending on location of the receiving pacemaker andpredetermined system functionality.

Also shown in FIG. 2 , the primary battery 114 has positive terminal 140and negative terminal 142. Current from the positive terminal 140 ofprimary battery 114 flows through a shunt 144 to a regulator circuit 146to create a positive voltage supply 148 suitable for powering theremaining circuitry of the pacemaker 102. The shunt 144 enables thebattery current monitor 136 to provide the processor 112 with anindication of battery current drain and indirectly of device health. Theillustrative power supply can be a primary battery 114.

In various embodiments, LP 102, 104 can manage power consumption to drawlimited power from the battery, thereby reducing device volume. Eachcircuit in the system can be designed to avoid large peak currents. Forexample, cardiac pacing can be achieved by discharging a tank capacitor(not shown) across the pacing electrodes. Recharging of the tankcapacitor is typically controlled by a charge pump circuit. In aparticular embodiment, the charge pump circuit is throttled to rechargethe tank capacitor at constant power from the battery.

In some embodiments, the controller 112 in one leadless cardiacpacemaker 102 can access signals on the electrodes 108 and can examineoutput pulse duration from another pacemaker for usage as a signaturefor determining triggering information validity and, for a signaturearriving within predetermined limits, activating delivery of a pacingpulse following a predetermined delay of zero or more milliseconds. Thepredetermined delay can be preset at manufacture, programmed via anexternal programmer, or determined by adaptive monitoring to facilitaterecognition of the triggering signal and discriminating the triggeringsignal from noise. In some embodiments or in some conditions, thecontroller 112 can examine output pulse waveform from another leadlesscardiac pacemaker for usage as a signature for determining triggeringinformation validity and, for a signature arriving within predeterminedlimits, activating delivery of a pacing pulse following a predetermineddelay of zero or more milliseconds.

FIG. 3 shows an LP 102, 104. The LP can include a hermetic housing 202with electrodes 108 a and 108 b disposed thereon. As shown, electrode108 a can be separated from but surrounded partially by a fixationmechanism 205, and the electrode 108 b can be disposed on the housing202. The fixation mechanism 205 can be a fixation helix, a plurality ofhooks, barbs, or other attaching features configured to attach thepacemaker to tissue, such as heart tissue.

The housing can also include an electronics compartment 210 within thehousing that contains the electronic components necessary for operationof the pacemaker, including, for example, a pulse generator,communication electronics, a battery, and a processor for operation. Thehermetic housing 202 can be adapted to be implanted on or in a humanheart, and can be cylindrically shaped, rectangular, spherical, or anyother appropriate shapes, for example.

The housing can comprise a conductive, biocompatible, inert, andanodically safe material such as titanium, 316L stainless steel, orother similar materials. The housing can further comprise an insulatordisposed on the conductive material to separate electrodes 108 a and 108b. The insulator can be an insulative coating on a portion of thehousing between the electrodes, and can comprise materials such assilicone, polyurethane, parylene, or another biocompatible electricalinsulator commonly used for implantable medical devices. In theembodiment of FIG. 3 , a single insulator 208 is disposed along theportion of the housing between electrodes 108 a and 108 b. In someembodiments, the housing itself can comprise an insulator instead of aconductor, such as an alumina ceramic or other similar materials, andthe electrodes can be disposed upon the housing.

As shown in FIG. 3 , the pacemaker can further include a header assembly212 to isolate 108 a and 108 b. The header assembly 212 can be made fromPEEK, tecothane or another biocompatible plastic, and can contain aceramic to metal feedthrough, a glass to metal feedthrough, or otherappropriate feedthrough insulator as known in the art.

The electrodes 108 a and 108 b can comprise pace/sense electrodes, orreturn electrodes. A low-polarization coating can be applied to theelectrodes, such as sintered platinum, platinum-iridium, iridium,iridium-oxide, titanium-nitride, carbon, or other materials commonlyused to reduce polarization effects, for example. In FIG. 3 , electrode108 a can be a pace/sense electrode and electrode 108 b can be a returnelectrode. The electrode 108 b can be a portion of the conductivehousing 202 that does not include an insulator 208.

Several techniques and structures can be used for attaching the housing202 to the interior or exterior wall of the heart. A helical fixationmechanism 205, can enable insertion of the device endocardially orepicardially through a guiding catheter. A torqueable catheter can beused to rotate the housing and force the fixation device into hearttissue, thus affixing the fixation device (and also the electrode 108 ain FIG. 3 ) into contact with stimulability tissue. Electrode 108 b canserve as an indifferent electrode for sensing and pacing. The fixationmechanism may be coated partially or in full for electrical insulation,and a steroid-eluting matrix may be included on or near the device tominimize fibrotic reaction, as is known in conventional pacingelectrode-leads.

Implant-to-Implant Event Messaging

LPs 102 and 104 can utilize implant-to-implant (i2i) communicationthrough event messages to coordinate operation with one another invarious manners. The terms i2i communication, i2i event messages, andi2i even markers are used interchangeably herein to refer to eventrelated messages and IMD/IMD operation related messages transmitted froman implanted device and directed to another implanted device (althoughexternal devices, e.g., a programmer, may also receive i2i eventmessages). In certain embodiments, LP 102 and LP 104 operate as twoindependent leadless pacers maintaining beat-to-beat dual-chamberfunctionality via a “Master/Slave” operational configuration. Fordescriptive purposes, the ventricular LP 104 shall be referred to as“vLP” and the atrial LP 102 shall be referred to as “aLP”. LP 102, 104that is designated as the master device (e.g. vLP) may implement all ormost dual-chamber diagnostic and therapy determination algorithms. Forpurposes of the following illustration, it is assumed that the vLP is a“master” device, while the aLP is a “slave” device. Alternatively, theaLP may be designated as the master device, while the vLP may bedesignated as the slave device. The master device orchestrates most orall decision-making and timing determinations (including, for example,rate-response changes).

In accordance with certain embodiments, methods are provided forcoordinating operation between first and second leadless pacemakers(LPs) configured to be implanted entirely within first and secondchambers of the heart. A method transmits an event marker throughconductive communication through electrodes located along a housing ofthe first LP, the event marker indicative of one of a local paced orsensed event. The method detects, over a sensing channel, the eventmarker at the second LP. The method identifies the event marker at thesecond LP based on a predetermined pattern configured to indicate thatan event of interest has occurred in a remote chamber. In response tothe identifying operation, the method initiates a related action in thesecond LP.

FIG. 4 is a timing diagram 400 demonstrating one example of an i2icommunication for a paced event. The i2i communication may betransmitted, for example, from LP 102 to LP 104. As shown in FIG. 4 , inthis embodiment, an i2i transmission 402 is sent prior to delivery of apace pulse 404 by the transmitting LP (e.g., LP 102). This enables thereceiving LP (e.g., LP 104) to prepare for the remote delivery of thepace pulse. The i2i transmission 402 includes an envelope 406 that mayinclude one or more individual pulses. For example, in this embodiment,envelope 406 includes a low frequency pulse 408 followed by a highfrequency pulse train 410. Low frequency pulse 408 lasts for a periodT_(i2iLF), and high frequency pulse train 410 lasts for a periodT_(i2iHF). The end of low frequency pulse 408 and the beginning of highfrequency pulse train 410 are separated by a gap period, T_(i2iGap).

As shown in FIG. 4 , the i2i transmission 402 lasts for a period Ti2iP,and pace pulse 404 lasts for a period Tpace. The end of i2i transmission402 and the beginning of pace pulse 404 are separated by a delay period,TdelayP. The delay period may be, for example, between approximately 0.0and 10.0 milliseconds (ms), particularly between approximately 0.1 msand 2.0 ms, and more particularly approximately 1.0 ms. The termapproximately, as used herein, means+/−10% of a specified value.

FIG. 5 is a timing diagram 500 demonstrating one example of an i2icommunication for a sensed event. The i2i communication may betransmitted, for example, from LP 102 to LP 104. As shown in FIG. 5 , inthis embodiment, the transmitting LP (e.g., LP 102) detects the sensedevent when a sensed intrinsic activation 502 crosses a sense threshold504. A predetermined delay period, T_(delayS), after the detection, thetransmitting LP transmits an i2i transmission 506 that lasts apredetermined period T_(i2iS). The delay period may be, for example,between approximately 0.0 and 10.0 milliseconds (ms), particularlybetween approximately 0.1 ms and 2.0 ms, and more particularlyapproximately 1.0 ms.

As with i2i transmission 402, i2i transmission 506 may include anenvelope that may include one or more individual pulses. For example,similar to envelope 406, the envelope of i2i transmission 506 mayinclude a low frequency pulse followed by a high frequency pulse train.

Optionally, wherein the first LP is located in an atrium and the secondLP is located in a ventricle, the first LP produces an AS/AP eventmarker to indicate that an atrial sensed (AS) event or atrial paced (AP)event has occurred or will occur in the immediate future. For example,the AS and AP event markers may be transmitted following thecorresponding AS or AP event. Alternatively, the first LP may transmitthe AP event marker slightly prior to delivering an atrial pacing pulse.Alternatively, wherein the first LP is located in an atrium and thesecond LP is located in a ventricle, the second LP initiates anatrioventricular (AV) interval after receiving an AS or AP event markerfrom the first LP; and initiates a post atrial ventricular blanking(PAVB) interval after receiving an AP event marker from the first LP.

Optionally, the first and second LPs may operate in a “pure”master/slave relation, where the master LP delivers “command” markers inaddition to or in place of “event” markers. A command marker directs theslave LP to perform an action such as to deliver a pacing pulse and thelike. For example, when a slave LP is located in an atrium and a masterLP is located in a ventricle, in a pure master/slave relation, the slaveLP delivers an immediate pacing pulse to the atrium when receiving an APcommand marker from the master LP.

In accordance with some embodiments, communication and synchronizationbetween the aLP and vLP is implemented via conducted communication ofmarkers/commands in the event messages (per i2i communication protocol).As explained above, conducted communication represents event messagestransmitted from the sensing/pacing electrodes at frequencies outsidethe RF or Wi-Fi frequency range. Alternatively, the event messages maybe conveyed over communication channels operating in the RF or Wi-Fifrequency range. The figures and corresponding description belowillustrate non-limiting examples of markers that may be transmitted inevent messages. The figures and corresponding description below alsoinclude the description of the markers and examples of results thatoccur in the LP that receives the event message. Table 1 representsexemplary event markers sent from the aLP to the vLP, while Table 2represents exemplary event markers sent from the vLP to the aLP. In themaster/slave configuration, AS event markers are sent from the aLP eachtime that an atrial event is sensed outside of the post ventricularatrial blanking (PVAB) interval or some other alternatively-definedatrial blanking period. The AP event markers are sent from the aLP eachtime that the aLP delivers a pacing pulse in the atrium. The aLP mayrestrict transmission of AS markers, whereby the aLP transmits AS eventmarkers when atrial events are sensed both outside of the PVAB intervaland outside the post ventricular atrial refractory period (PVARP) orsome other alternatively-defined atrial refractory period.Alternatively, the aLP may not restrict transmission of AS event markersbased on the PVARP, but instead transmit the AS event marker every timean atrial event is sensed.

TABLE 1 “A2V” Markers/Commands (i.e., from aLP to vLP) MarkerDescription Result in vLP AS Notification of a sensed event Initiate AVinterval in atrium (if not in PVAB or (if not in PVAB or PVARP) PVARP)AP Notification of a paced Initiate PAVB event in atrium Initiate AVinterval (if not in PVARP)

As shown in Table 1, when an aLP transmits an event message thatincludes an AS event marker (indicating that the aLP sensed an intrinsicatrial event), the vLP initiates an AV interval timer. If the aLPtransmits an AS event marker for all sensed events, then the vLP wouldpreferably first determine that a PVAB or PVARP interval is not activebefore initiating an AV interval timer. If however the aLP transmits anAS event marker only when an intrinsic signal is sensed outside of aPVAB or PVARP interval, then the vLP could initiate the AV intervaltimer upon receiving an AS event marker without first checking the PVABor PVARP status. When the aLP transmits an AP event marker (indicatingthat the aLP delivered or is about to deliver a pace pulse to theatrium), the vLP initiates a PVAB timer and an AV interval time,provided that a PVARP interval is not active. The vLP may also blank itssense amplifiers to prevent possible crosstalk sensing of the remotepace pulse delivered by the aLP.

TABLE 2 “V2A” Markers/Commands (i.e., from vLP to aLP) MarkerDescription Result in aLP VS Notification of a Initiate PVARP sensedevent in ventricle VP Notification of a paced Initiate PVAB event inventricle Initiate PVARP AP Command to deliver Deliver immediateimmediate pace pulse pace pulse to atrium in atrium

As shown in Table 2, when the vLP senses a ventricular event, the vLPtransmits an event message including a VS event marker, in response towhich the aLP may initiate a PVARP interval timer. When the vLP deliversor is about to deliver a pace pulse in the ventricle, the vLP transmitsVP event marker. When the aLP receives the VP event marker, the aLPinitiates the PVAB interval timer and also the PVARP interval timer. TheaLP may also blank its sense amplifiers to prevent possible crosstalksensing of the remote pace pulse delivered by the vLP. The vLP may alsotransmit an event message containing an AP command marker to command theaLP to deliver an immediate pacing pulse in the atrium upon receipt ofthe command without delay.

The foregoing event markers are examples of a subset of markers that maybe used to enable the aLP and vLP to maintain full dual chamberfunctionality. In one embodiment, the vLP may perform all dual-chamberalgorithms, while the aLP may perform atrial-based hardware-relatedfunctions, such as PVAB, implemented locally within the aLP. In thisembodiment, the aLP is effectively treated as a remote ‘wireless’ atrialpace/sense electrode. In another embodiment, the vLP may perform mostbut not all dual-chamber algorithms, while the aLP may perform a subsetof diagnostic and therapeutic algorithms. In an alternative embodiment,vLP and aLP may equally perform diagnostic and therapeutic algorithms.In certain embodiments, decision responsibilities may be partitionedseparately to one of the aLP or vLP. In other embodiments, decisionresponsibilities may involve joint inputs and responsibilities.

In an embodiment, ventricular-based pace and sense functionalities arenot dependent on any i2i communication, in order to provide safertherapy. For example, in the event that LP to LP (i2i) communication islost (prolonged or transient), the system 100 may automatically revertto safe ventricular-based pace/sense functionalities as the vLP deviceis running all of the necessary algorithms to independently achievethese functionalities. For example, the vLP may revert to a WI mode asthe vLP does not depend on i2i communication to perform ventricularpace/sense activities. Once i2i communication is restored, the system100 can automatically resume dual-chamber functionalities.

Mitigating Excessive Wakeups in Dual Chamber Leadless Pacemaker

As explained above, each of LPs 102 and 104 may include first and secondreceivers 120 and 122 that operate with different first and secondactivation protocols and different first and second receive channels. Asalso explained above, the first and second receivers 120 and 122 of eachof the LPs 102 and 104 can enable the LPs 102 and 104 to implement astaged receiver wakeup scheme in order to improve reliability yet remainpower efficient. For example, the first receiver 120 may be assigned afirst activation protocol that by default causes the first receiver 120to be normally “on” or “awake” or “active” (which terms are usedinterchangeably herein) and listening for messages received over a firstreceive channel that has a lower fundamental frequency range/pulseduration (e.g., 1 kHz to 100 kHz/10 μs to approximately 1 ms) ascompared to a fundamental frequency range (e.g., greater than 100kHz/less than 10 μs per pulse) assigned to the second receive channel.The first receiver 120 may maintain the first channel active for atleast a portion of a time when the second channel is inactive, so thatthe first receiver 120 can listen for event messages from a remote LP.The controller or processor of the LP can determine whether the incomingsignal received over the first channel corresponds to an LP wakeupnotice. The second receiver 122 may be assigned a second activationprotocol that is a triggered protocol, in which the second receiver 122is normally “off” or “asleep” or “inactive” (which terms are usedinterchangeably herein) and becomes active in response to detection oftrigger events over the first receive channel (e.g., when the incomingsignal corresponds to the LP wakeup notice, activating the secondchannel at the local LP). In other words, in order to conserve power thesecond receiver 122 can be asleep unless awaken by the first receiver120. Depending upon implementation, when the second receiver 122 isasleep, it can either be in a low power mode or completely disconnectedfrom a power supply. Regardless of the implementation, the secondreceiver 122 will consume less power when it is asleep compared to whenit is awake. Similarly, the first receiver 120 will consume less powerwhen it is asleep compared to when it is awake. When both the first andsecond receivers are awake the second receiver consumes more power thanthe first receiver.

The first receiver 120 of a given LP (e.g., 102) can also be referred toas a low power low bandwidth receiver, since it is configured to operateat a lower power and a lower bandwidth than the second receiver 122 doeswhen the second receiver 122 is awake. Conversely, the second receiver122 of the LP (e.g., 102) can also be referred to as a high power highbandwidth receiver, since it is configured to operate at a higher powerand a higher bandwidth than the first receiver 120 does when the secondreceiver 122 is awake. In accordance with certain embodiments of thepresent technology, in order to conserve power, as part of i2icommunication, a signal received by the low power low bandwidth receiver(i.e., the first receiver 120) is used to wakeup the high power highbandwidth receiver (i.e., the second receiver 122), using what can bereferred to as a two-step wakeup process. In the two-step wakeupprocess, the first receiver 120 of a device (e.g., the LP 102) can benormally awake and listening for messages while the second receiver 122is normally asleep and only woken up by the first receiver 120 when thefirst receiver 120 receives a portion of a message (e.g., the lowfrequency pulse 408) that also includes another portion (e.g., the highfrequency pulse train 416) that is to be received and decoded using thesecond receiver 122.

A potential problem with the aforementioned two-step wakeup process isthat the low power low bandwidth receiver (i.e., the first receiver 120)may be very sensitive to electrical noise, such as, but not limited to,electromagnetic interference (EMI). More specifically, in anelectrically noisy environment, the high sensitivity of the firstreceiver 120 to electrical noise may cause the first receiver 120 tofrequently trigger wakeups of the second receiver 122 when unnecessary.This can lead to significant power consumption and a shorter batterylife of the LP, and thus, a reduction in the useful life of the LP(e.g., 102). A triggered wakeup of the second receiver 122 is consideredunnecessary, for example, where the wakeup was triggered in response tonoise that was mistaken for a valid message, as opposed to beingtriggered in response to an actual valid message being received fromanother LP (e.g., 104). Exemplary types of valid messages that an LP(e.g., 102) can receive from another LP (e.g., 104) include, but are notlimited to, the event messages that were described above with referenceto FIGS. 1-5 and Tables 1 and 2.

Certain embodiments of the present technology, which are describedbelow, mitigate and preferably prevent the first receiver 120 fromunnecessarily waking up the second receiver 122 of a device, such as anLP (e.g., 102). Such embodiments are beneficial because they can reducepower consumption and increase battery life of the LP, and thus,increase the useful life of the LP (e.g., 102).

Even with various layers of data integrity protection, there is stillthe relatively low possibility that noise may be detected as a validmessage, resulting in a false positive. For example, noise that isreceived and is mistaken for being an actual message and is decoded bythe IMD because the noise is sufficiently similar to an actual messageis an example of how a false positive can occur. In accordance withcertain embodiments of the present technology, monitoring for messagesis temporarily suspended when it is determined that an unacceptableamount of noise is present, thereby reducing the probability that afalse positive detection of a message occurs.

In certain embodiments, if the first receiver 120 triggers the wakeup ofthe second receiver 122, but the triggered wakeup is not followed(within a specified amount of time) by the second receiver 122 receivingand decoding a valid message, then the wakeup is considered invalid, ormore generally, the received message that caused the first receiver 120to wakeup the second receiver 122 can be considered an invalid message.

In accordance with certain embodiments, a device (e.g., the LP 102)temporarily disables at least one of its communication capabilities whenan amount of invalid messages received during a message alert periodreaches (e.g., equals or exceeds) a specified threshold. The periodduring which the device temporarily disables at least one of itscommunication capabilities is often referred to herein as a disableperiod. In accordance with certain embodiments, during the disableperiod the device enters a Noise State. While in the Noise State, whichcan also be referred to as a noise reversion state, or a communicationnoise reversion state, the device can operate in a safe pacing mode(e.g., VVI or VOO) that does not depend on i2i communication. After thedisable period expires, i.e., has ended, the device can return toattempting to detect a valid message during a next message alert period,and may trigger another disable period if again an amount of invalidmessages received during the message alert period reaches a specifiedthreshold (which can be the same threshold, or a different thresholdthan used in the preceding message alert period).

In certain embodiments, the device can exit the Noise State whenever thedisable period expires. Alternatively, and preferably, once the deviceenters the Noise State, the device remains in the Noise State (duringwhich time the device operates in a safe pacing mode) until one validmessage is (or some other specified number of valid messages are)received, at which point the device exits the Noise State and returns toits normal pacing mode.

The above summarized embodiments can be used to mitigate and preferablyprevent a first receiver (e.g., 120) from unnecessarily waking up asecond receiver (e.g., 122) of a device, such as an LP (e.g., 102). Suchembodiments can also be used to reduce the chance of an invalid messagebeing mistaken for being a valid message. In other words, suchembodiments can be used to reduce false positive detections of validmessages. By temporarily disabling a communication capability (e.g., thefirst receiver 120 itself, its input and/or its output) of a device(e.g., LP 102), and/or reducing how often a first receiver (e.g., 120)unnecessarily wakes up a second receiver (e.g., 122) of a device, suchas an LP (e.g., 102), embodiments of the present technology can be usedto conserve power and thus improve battery and device longevity. Certainsuch embodiments of the present technology are described below withreference to the high level flow diagram of FIG. 6A. The methodsdescribed with reference to FIG. 6A, and with reference to FIG. 6B, canbe performed under the control of a processor or controller (e.g., 112in FIG. 2 , or 720 in FIG. 7 ). In other words, a processor orcontroller can be configured to perform various aspects of the presenttechnology.

Referring to FIG. 6A, block 600, labeled “Start”, is the entry point forthe method. At a step 602, an invalid message count is set, or reset, toits initial value, which can be zero, but is not limited thereto. Atstep 604 there is a determination of whether a next message alert periodhas begun, wherein the message alert period is a period during which anIMD that is performing the method monitors for a message (i.e., listensfor a message). In certain embodiments, a message alert period isrelated to a cardiac cycle, and may occur during an entire cardiaccycle, or just a portion of a cardiac cycle. For example, where an IMDperforming the method is implanted in a ventricle, a message alertperiod can be a portion of a cardiac cycle that follows an AV delay, ablanking period and/or a relative refractory period, but is not limitedthereto. In such an embodiment, if the decision at step 604 occurs,e.g., during an AV delay or a blanking period, then the answer to thedecision at step 604 would be No, and step 604 would be repeated in aloop until the answer to the decision at step 604 is Yes, at which pointflow would go to step 606. For another example, where an IMD performingthe method is implanted in an atrium, a message alert period can be aportion of a cardiac cycle that follows a post ventricular atrialblanking (PVAB) period, a post ventricular atrial refractory period(PVARP) and/or some other alternatively-defined atrial refractoryperiod. In such an embodiment, if the decision at step 604 occurs, e.g.,during an atrial blanking or refractory period, then the answer to thedecision at step 604 would be No, and step 604 would be repeated in aloop until the answer to the decision at step 604 is Yes, at which pointflow would go to step 606.

At step 606, a communication capability of the IMD is enabled. Referringbriefly back to FIG. 2 , in accordance with certain embodiments, thecommunication capability that is enabled at step 606 can relate to thefirst receiver 120 of the IMD, and more specifically, can be thereceiver 120 itself, an input to the first receiver 120, or an outputfrom the first receiver 120.

At step 608, a message is monitored for (e.g., listened for) by the IMD,and more specifically, by a receiver (e.g., the first receiver 120) ofthe IMD (e.g., an LP 102 or 104).

At step 610 there is a determination of whether a message was received.If the answer to the determination at step 610 is No (i.e., if a messagewas not received), then at step 620 there is a determination of whetherthe message alert period has ended. If the answer to the determinationat step 620 is No (i.e., if the message alert period has not ended),then flow returns to step 608. If the answer to the determination atstep 620 is Yes (i.e., if the message alert period has ended), then flowreturns to step 602. In accordance with certain embodiments, in order toconserver power, and thus a battery and/or device life, during theperiod of time between when a message alert period has ended and when anext message alert period begins, a receiver and/or transmitter (andor/one or more other components of an IMD) can be disabled or put into alow power mode.

If the answer to the determination at step 610 is Yes (i.e., if amessage was received), then at step 612 there is a determination ofwhether the received message is valid. The term “message”, as usedherein, can refer to an actual sent message that is received and iscapable of being decoded by the second receiver 122, an actual sentmessage that is received but is too noisy to be decoded by the secondreceiver 122, an actual sent message that is received but due to noiseit is decoded mistakenly for a different message, noise that isinitially mistaken for being an actual message but is sufficientlydifferent than an actual message so that it cannot be decoded by thesecond receiver 122, as well as noise that is received and is mistakenfor being an actual message and is decoded by the IMD because the noiseis sufficiently similar to an actual message. The term “valid message”,as used herein, can refer to an actual sent message that is received andis capable of being decoded by the second receiver 122, an actual sentmessage that is received but due to noise it is decoded mistakenly for adifferent message (this may occur in rare circumstances), or noise thatis received and is mistaken for being an actual message and is decodedby the IMD because the noise is sufficiently similar to an actualmessage (this may occur in very rare circumstances). The latter twotypes of a “valid message”, which may occur in rare or very rarecircumstances, are examples false positives. Accordingly, it is possiblethat a “valid message” is not an actual message, or is an actual messagethat has been decoded incorrectly. The term “invalid message”, as usedherein, can refer to an actual sent message that is received but is toonoisy to be decoded by the second receiver 122, as well as noise that isinitially mistaken for being an actual message but is sufficientlydifferent than an actual message so that it cannot be decoded by thesecond receiver 122. In accordance with certain embodiments, thedetermination of whether a message is valid or invalid can be performedby a processor or controller that performs decoding and error detectionor correction.

At step 614 there is a determination of whether the received message wasdetermined to be valid at step 612. While steps 614 and 612 are shown asseparate steps in FIG. 6A, these two steps could have instead been shownas a single step. For example, the block labeled 620 in FIG. 6A can beremoved and the “No” path from block 610 can instead go to block 618.For another example, the block labeled 618 in FIG. 6A can be removed andflow can go directly from block 616 to block 620.

Still referring to FIG. 6A, if the answer to the determination at step614 is No (i.e., if a valid message was not received), then flow goes tostep 622, and the received message (which was determined to have beennot valid, or invalid) is ignored. At step 624 the invalid message countis incremented. For example, the equation imc=imc+1 can be used at step624, where imc is the invalid message count, which is set or reset eachtime step 602 is performed. At step 626 the invalid message count iscompared to an invalid massage count threshold (imct), and at step 628that is a determination of whether the invalid message count threshold(imct) has been reached. If the answer to the determination at step 628is No (i.e., if the invalid message count threshold has not beenreached), then flow returns to step 608 and monitoring for anothermessage occurs. If the answer to the determination at step 628 is Yes(i.e., if the invalid message count threshold has been reached), that isindicative of electromagnetic interference (EMI) and/or other noisebeing present, and thus, at step 630 the communication capability (thatwas enabled at step 606) is disabled for a disable period. While steps626 and 628 are shown as two separate steps, those steps canalternatively be combined into a single step.

The disable period, which is a period during which a communicationcapability of the device performing the method is disabled, can bespecified in units of time, e.g., a specified number of seconds. Forexample, the disable period can be 2 seconds, 4 seconds, or 10 seconds,but is not limited thereto. Alternatively, the disable period can bespecified as a number (N) of cardiac cycles, or other types of cycles,where N is an integer that is equal to or greater than 1. For example,the disable period can be 2 cardiac cycles, 4 cardiac cycles, or 10cardiac cycles, but is not limited thereto. Where the method beingdescribed is performed independently by an LP 102 implanted in anatrium, as well as by an LP 104 implanted in a ventricle, what the LP102 considers a cardiac cycle may differ from what the LP 104 considersa cardiac cycle, because the LPs 102 and 104 have different frames ofreference. For example, the LP 102 may consider a cardiac cycle as theperiod between two atrial (paced or sensed) events, whereas the LP 104may consider a cardiac cycle as the period between two ventricular(paced or sensed) events.

After the communication capability is disabled at step 630, then flowgoes to step 632 where there is a determination of whether the disableperiod has expired. Until the disable period expires, step 632 isrepeated in a loop until the answer to the decision at step 632 is Yes,at which point flow would return to step 602, as shown in FIG. 6A.

At step 630, the communication capability of the IMD that is disabledcan be a communication capability related to a receiver and/or atransmitter of the IMD. For example, referring briefly back to FIG. 2 ,in accordance with certain embodiments, the communication capabilitythat is disabled at step 630 can relate to the first receiver 120 of theIMD, and more specifically, can be the first receiver 120 itself, aninput to the first receiver 120, and/or an output from the firstreceiver 120. For example, disabling the communication capabilityrelated to the first receiver 120 of the IMD, at step 630, can involvedisconnecting the input to the first receiver 120, forcing the output ofthe first receiver 120 inactive, and/or ignoring the output of the firstreceiver 120. In other words, at step 630 the first receiver 120 itselfcan be disabled, the input to the first receiver 120 can be disabled bydisconnecting the input, and/or an output from the first receiver 120can be disabled by forcing the output of the first receiver 120 inactiveand/or ignoring the output of the first receiver 120. Other variationsare also possible and within the scope of the embodiments describedherein. Additionally, in accordance with certain embodiments, acommunication capability related to the transmitter of the IMD (e.g.,118 in FIG. 2 ) can be disabled during the disable period, which in oneembodiment may be achieved by not activating the transmitter during thedisable period.

Returning to the discussion of step 614 in FIG. 6A, if the answer to thedetermination at step 614 is Yes (i.e., if a valid message wasreceived), then flow goes to step 616, and information included in thevalid message is acted upon. Where the IMD (e.g., LP 104) performing themethod is implanted in a ventricle, the information included in thevalid message (e.g., received from another IMD, e.g., LP 102, implantedin an atrium) can be an atrial sense (AS) notification of a sensed eventin atrium that causes the IMD to initiate an AV interval, or an atrialpace (AP) notification of a paced event in atrium that causes the IMD toinitiate a post ventricular atrial blanking (PVAB) interval, some otheralternatively-defined atrial blanking period, or an AV interval (if notin PVARP). Where the IMD (e.g., LP 102) performing the method isimplanted in an atrium, the information included in the valid message(e.g., received from another IMD, e.g., LP 104, implanted in aventricle) can be a ventricular sense (VS) notification of a sensedevent in a ventricle that causes the IMD to initiate a PVARP interval,or an ventricular pace (VP) notification of a paced event in ventriclethat causes the IMD to initiate a PVAB interval or a PVARP interval, oran atrial pace (AP) command that causes the IMD to immediately deliver apace pulse in the atrium. These are just a few examples, which are notintended to be all encompassing.

Still referring to FIG. 6A, after (or while) step 616 is beingperformed, at step 618 there is a determination of whether the messagealert period has ended. If the answer to the determination at step 620is No (i.e., if the message alert period has not ended), then flowreturns to step 608. If the answer to the determination at step 620 isYes (i.e., if the message alert period has ended), then flow returns tostep 602. As can be appreciated from FIG. 6A, step 618 and 620 are thesame, and thus, the flow diagram in FIG. 6A can be redrawn to includejust one of those steps, as was explained above when discussing step618. In certain embodiments it is possible that more than one validmessage can be received during a same message alert period. For example,if an LP (e.g., 104) implanted within a ventricle detects an R wave andsoon thereafter detects a premature ventricular contraction (PVC), thismay result in another LP (e.g., 102) implanted within an atriumreceiving more than one valid message within a same message alertperiod.

The invalid message count threshold (imct), referred to at steps 626 and628, can be a value that is either set by default or by a physician orclinician, which once set, is not changed on the fly by the IMD that isperforming the method summarized with reference to FIG. 6A. Inalternative embodiments, described below with reference to FIG. 6B, theIMD can change the invalid message count threshold (imct) on the fly, independence on whether a valid message was detected during an immediatelypreceding message alert period. More specifically, the invalid messagecount threshold (imct) can be reduced if a valid message was notdetected during an immediately preceding message alert period, comparedto if a valid message was detected during the immediately precedingmessage alert period. Accordingly, this method variant effectively makesit more difficult for the IMD to exit from a Noise State that the IMDenters during the disable period, assuming the IMD is configured toremain in the Noise State (once the Noise State is entered) until avalid message (or a specified number of valid messages) are thereafterreceived. Alternatively, the invalid message count threshold (imct) canbe increased if a valid message was not detected during an immediatelypreceding message alert period, compared to if a valid message wasdetected during the immediately preceding message alert period. Moregenerally, in certain embodiments the invalid message count thresholdcan be specified in dependence on whether a valid message was detectedduring an immediately preceding message alert period.

Referring to FIG. 6B, most of the steps shown therein are the same asthe steps shown in and described above with reference to FIG. 6A, andthus, such steps are labeled the same and need not be described again. Acomparison between FIGS. 6A and 6B shows that steps 601, 617, and 631are added in FIG. 6B. At step 601 the invalid message count threshold(imct) is set to a first value, i.e., imct₁. Similarly, at step 617,after a valid message has been received and acted upon, the invalidmessage count threshold (imct) is set to the same first value, i.e.,imct₁. By contrast, at step 631, the invalid message count threshold(imct) is set to a second value, i.e., imct₂. In accordance with certainembodiments, imct₂ is less than imct₁. As noted above, this methodvariant effectively makes it more difficult for the IMD to exit from aNoise State that the IMD enters during the disable period, assuming theIMD is configured to remain in the Noise State (once the Noise State isentered) until a valid message (or a specified number of valid messages)are thereafter received. The method variant described with reference toFIG. 6B provides for hysteresis and biases the method away from apremature exit from the Noise State, assuming the IMD is configured toremain in the Noise State (once the Noise State is entered) until avalid message (or a specified number of valid messages) are thereafterreceived.

In alternative embodiments, rather than modifying the invalid messagecount threshold (imct) based on whether a valid message was receivedduring an immediately preceding message alert period, an amount by whichthe invalid message count is incremented (in response an invalid messagebeing received) can be modified. For example, in accordance with anembodiment, an amount by which the invalid message count is incrementedin response to determining that a message received during a messagealert period is invalid, can be greater if a valid message was notdetected during an immediately preceding message alert period, comparedto if a valid message was detected during the immediately precedingmessage alert period. Other variations are also possible and within thescope of the embodiments of the present technology described herein.

In accordance with certain embodiments, the invalid message countthreshold (imct) is modified based on temporal information about invalidmessages that were received. For example, where two invalid messages arereceived within a specified relatively short time period (and thus,within in rapid succession), that can be interpreted as being indicativeof being caused by excessive interference. Thus, when this occurs, theinvalid message count threshold (e.g., referred to in steps 626 and 628in FIG. 6A) can be reduced so that a decision to enter the disableperiod (and simultaneously a Noise State) can occur in response toreceiving relatively view invalid message.

Alternatively, an amount by which the invalid message count isincremented (e.g., at step 624 in FIG. 6A) can be modified based ontemporal information about invalid messages that were received. Forexample, where two invalid messages are received within a specifiedrelatively short time period (and thus, in rapid succession), that canbe interpreted as being indicative of being caused by excessiveinterference, as noted above. Thus, when this occurs, the amount bywhich the invalid message count is incremented (e.g., at instances ofstep 624 in FIG. 6A) can be increased so that a decision to enter thedisable period (and simultaneously a Noise State) can occur in responseto receiving relatively few invalid message.

Whenever an IMD enters a disable period, and then after exiting adisable period again enters another disable period without receiving avalid message therebetween, it can be assumed that the interference orother noise (that prevented at least one valid message from beingreceived during a message alert period) has continued to persist. Inother words, if no valid message is received for two or more consecutivemessage alert periods, then it is assumed that persistent interferenceor other noise exists. In accordance with certain embodiments, whenthere is persistent interference or other noise the length of thedisable period can be progressively increased. For example, an initialdisable period can be equal to 1 cardiac cycle (or 1 second). Then, ifno valid message is detected during the next message alert period (thatfollows the initial disable period), then the second disable period canbe 5 cardiac cycles (or 5 seconds). Thereafter, if no valid message isdetected during the following message alert period, then the thirddisable period can be 10 cardiac cycles (or 10 seconds). The process ofprogressively increasing the length of the disable period mightcontinue, up to a maximum number of cardiac cycles (or a maximum numberof seconds), if there are more consecutive message alert periods duringwhich no valid message is received. Once a valid message is detected itcan be assumed that the interference or other noise has subsided, andthe length of the disable period can be immediately returned to itsinitial length (e.g., 1 cardiac cycle, or 1 second). Alternatively, thelength of the disable period can be gradually stepped down to itsinitial or minimum length, just in case the subsiding of theinterference or other noise was only temporary. The stepped downprogression of the disable period that occurs in the absence ofinterference or other noise can follow the same trajectory (in reverse)as followed when no valid messages were received in multiple consecutivemessage alert periods, or the stepped down progression can follow adifferent trajectory that might recover faster (or slower) than thestepped up progression.

The length of a disable period can depend on alternative or additionalinformation. In accordance with certain embodiments, the disable period(or an initial disable period that can be increased based on receivingno valid messages in consecutive message alert periods) can be set basedon the current operational mode of the IMD that is performing themethod. In other words, a length of a disable period during which acommunication capability of an IMD is disabled, in response to theinvalid message count reaching the corresponding invalid message countthreshold, can depend on which one of a plurality of operational modesthe IMD is set to, and thus, operating in. For example: when the IMD isin its normal operation mode the disable period can be 5 cardiac cycles(or 5 seconds); when the IMD is in a magnetic resonance imaging (MRI)ready operational mode the disable period the disable period can be 300cardiac cycles (or 300 seconds); and when the IMD is in an RF ablationready operational mode the can be 100 cardiac cycles (or 100 seconds).These are just a few examples, which are not meant to be allencompassing, as there are other possible operational modes, and thereare other possible lengths for the disable period. The reason forincreasing the disable period when the IMD is in an MRI readyoperational mode is that it is expected that once the IMD experiencesinterference due to an MRI system, that interference is likely to lastquite a while before it subsides. Similarly, interference caused by anRF ablation system would likely occur for a while, but not likely aslong as would occur due to an MRI system.

As noted above, in accordance with certain embodiments, during a disableperiod the device enters a Noise State, during which time the deviceoperates in a safe pacing mode (e.g., VVI or VOO) that does not dependon i2i (or other) communication. In certain embodiments, once the deviceenters the Noise State, the device remains in the Noise State (duringwhich time the device operates in a safe pacing mode) until a specifiednumber (that is greater than or equal to one) of valid messages arereceived. Preferably, the specified number is between one and five,inclusively, but is not limited thereto. The period or mode during whichthe IMD determines whether to exit the Noise State can be referred to asthe re-confirm period or the re-confirm mode. Such embodiments increasethe probability that interference has subsided before the devicetransitions from the Noise State back, during which a safe pacing modeis used, to its normal state or pacing mode (e.g., DDD, DDI, VDD, VDI,or DOO).

FIG. 7 shows a block diagram of one embodiment of an LP 701 that isimplanted into the patient as part of the implantable cardiac system inaccordance with certain embodiments herein. LP 701 may be implemented asa full-function biventricular pacemaker, equipped with both atrial andventricular sensing and pacing circuitry for four chamber sensing andstimulation therapy (including both pacing and shock treatment).Optionally, LP 701 may provide full-function cardiac resynchronizationtherapy. Alternatively, LP 701 may be implemented with a reduced set offunctions and components. For instance, the IMD may be implementedwithout ventricular sensing and pacing.

LP 701 has a housing 700 to hold the electronic/computing components.Housing 700 (which is often referred to as the “can”, “case”,“encasing”, or “case electrode”) may be programmably selected to act asthe return electrode for certain stimulus modes. Housing 700 may furtherinclude a connector (not shown) with a plurality of terminals 702, 704,706, 708, and 710. The terminals may be connected to electrodes that arelocated in various locations on housing 700 or elsewhere within andabout the heart. LP 701 includes a programmable microcontroller 720 thatcontrols various operations of LP 701, including cardiac monitoring andstimulation therapy. Microcontroller 720 includes a microprocessor (orequivalent control circuitry), RAM and/or ROM memory, logic and timingcircuitry, state machine circuitry, and I/O circuitry.

LP 701 further includes a first pulse generator 722 that generatesstimulation pulses for delivery by one or more electrodes coupledthereto. Pulse generator 722 is controlled by microcontroller 720 viacontrol signal 724. Pulse generator 722 may be coupled to the selectelectrode(s) via an electrode configuration switch 726, which includesmultiple switches for connecting the desired electrodes to theappropriate I/O circuits, thereby facilitating electrodeprogrammability. Switch 726 is controlled by a control signal 728 frommicrocontroller 720.

In the embodiment of FIG. 7 , a single pulse generator 722 isillustrated. Optionally, the IMD may include multiple pulse generators,similar to pulse generator 722, where each pulse generator is coupled toone or more electrodes and controlled by microcontroller 720 to deliverselect stimulus pulse(s) to the corresponding one or more electrodes.

Microcontroller 720 is illustrated as including timing control circuitry732 to control the timing of the stimulation pulses (e.g., pacing rate,atrioventricular (AV) delay, atrial interconduction (A-A) delay, orventricular interconduction (V-V) delay, etc.). Timing control circuitry732 may also be used for the timing of refractory periods, blankingintervals, noise detection windows, evoked response windows, alertintervals, marker channel timing, and so on. Microcontroller 720 alsohas an arrhythmia detector 734 for detecting arrhythmia conditions and amorphology detector 736. Although not shown, the microcontroller 720 mayfurther include other dedicated circuitry and/or firmware/softwarecomponents that assist in monitoring various conditions of the patient'sheart and managing pacing therapies. The microcontroller can include aprocessor. The microcontroller, and/or the processor thereof, can beused to perform the methods of the present technology described herein.

LP 701 is further equipped with a communication modem(modulator/demodulator) 740 to enable wireless communication with theremote slave pacing unit. Modem 740 may include one or more transmittersand two or more receivers as discussed herein in connection with FIG.1B. In one implementation, modem 740 may use low or high frequencymodulation. As one example, modem 740 may transmit i2i messages andother signals through conductive communication between a pair ofelectrodes. Modem 740 may be implemented in hardware as part ofmicrocontroller 720, or as software/firmware instructions programmedinto and executed by microcontroller 720. Alternatively, modem 740 mayreside separately from the microcontroller as a standalone component.

LP 701 includes a sensing circuit 744 selectively coupled to one or moreelectrodes, that perform sensing operations, through switch 726 todetect the presence of cardiac activity in the right chambers of theheart. Sensing circuit 744 may include dedicated sense amplifiers,multiplexed amplifiers, or shared amplifiers. It may further employ oneor more low power, precision amplifiers with programmable gain and/orautomatic gain control, bandpass filtering, and threshold detectioncircuit to selectively sense the cardiac signal of interest. Theautomatic gain control enables the unit to sense low amplitude signalcharacteristics of atrial fibrillation. Switch 726 determines thesensing polarity of the cardiac signal by selectively closing theappropriate switches. In this way, the clinician may program the sensingpolarity independent of the stimulation polarity.

The output of sensing circuit 744 is connected to microcontroller 720which, in turn, triggers or inhibits the pulse generator 722 in responseto the presence or absence of cardiac activity. Sensing circuit 744receives a control signal 746 from microcontroller 720 for purposes ofcontrolling the gain, threshold, polarization charge removal circuitry(not shown), and the timing of any blocking circuitry (not shown)coupled to the inputs of the sensing circuitry.

In the embodiment of FIG. 7 , a single sensing circuit 744 isillustrated. Optionally, the IMD may include multiple sensing circuits,similar to sensing circuit 744, where each sensing circuit is coupled toone or more electrodes and controlled by microcontroller 720 to senseelectrical activity detected at the corresponding one or moreelectrodes. Sensing circuit 744 may operate in a unipolar sensingconfiguration or in a bipolar sensing configuration.

LP 701 further includes an analog-to-digital (ND) data acquisitionsystem (DAS) 750 coupled to one or more electrodes via switch 726 tosample cardiac signals across any pair of desired electrodes. Dataacquisition system 750 is configured to acquire intracardiac electrogramsignals, convert the raw analog data into digital data, and store thedigital data for later processing and/or telemetric transmission to anexternal device 754 (e.g., a programmer, local transceiver, or adiagnostic system analyzer). Data acquisition system 750 is controlledby a control signal 756 from the microcontroller 720.

Microcontroller 720 is coupled to a memory 760 by a suitabledata/address bus. The programmable operating parameters used bymicrocontroller 720 are stored in memory 760 and used to customize theoperation of LP 701 to suit the needs of a particular patient. Suchoperating parameters define, for example, pacing pulse amplitude, pulseduration, electrode polarity, rate, sensitivity, automatic features,arrhythmia detection criteria, and the amplitude, waveshape and vectorof each shocking pulse to be delivered to the patient's heart withineach respective tier of therapy.

The operating parameters of LP 701 may be non-invasively programmed intomemory 760 through a telemetry circuit 764 in telemetric communicationvia communication link 766 with external device 754. Telemetry circuit764 allows intracardiac electrograms and status information relating tothe operation of LP 701 (as contained in microcontroller 720 or memory760) to be sent to external device 754 through communication link 766.

LP 701 can further include magnet detection circuitry (not shown),coupled to microcontroller 720, to detect when a magnet is placed overthe unit. A magnet may be used by a clinician to perform various testfunctions of LP 701 and/or to signal microcontroller 720 that externaldevice 754 is in place to receive or transmit data to microcontroller720 through telemetry circuits 764.

LP 701 can further include one or more physiological sensors 770. Suchsensors are commonly referred to as “rate-responsive” sensors becausethey are typically used to adjust pacing stimulation rates according tothe exercise state of the patient. However, physiological sensor 770 mayfurther be used to detect changes in cardiac output, changes in thephysiological condition of the heart, or diurnal changes in activity(e.g., detecting sleep and wake states). Signals generated byphysiological sensors 770 are passed to microcontroller 720 foranalysis. Microcontroller 720 responds by adjusting the various pacingparameters (such as rate, AV Delay, V-V Delay, etc.) at which the atrialand ventricular pacing pulses are administered. While shown as beingincluded within LP 701, physiological sensor(s) 770 may be external toLP 701, yet still be implanted within or carried by the patient.Examples of physiologic sensors might include sensors that, for example,sense respiration rate, pH of blood, ventricular gradient, activity,position/posture, minute ventilation (MV), and so forth.

A battery 772 provides operating power to all of the components in LP701. Battery 772 is capable of operating at low current drains for longperiods of time, and is capable of providing high-current pulses (forcapacitor charging) when the patient requires a shock pulse (e.g., inexcess of 2 A, at voltages above 2 V, for periods of 10 seconds ormore). Battery 772 also desirably has a predictable dischargecharacteristic so that elective replacement time can be detected. As oneexample, LP 701 employs lithium/silver vanadium oxide batteries.

LP 701 further includes an impedance measuring circuit 774, which can beused for many things, including: lead impedance surveillance during theacute and chronic phases for proper lead positioning or dislodgement;detecting operable electrodes and automatically switching to an operablepair if dislodgement occurs; measuring respiration or minuteventilation; measuring thoracic impedance for determining shockthresholds; detecting when the device has been implanted; measuringstroke volume; and detecting the opening of heart valves; and so forth.Impedance measuring circuit 774 is coupled to switch 726 so that anydesired electrode may be used. In this embodiment LP 701 furtherincludes a shocking circuit 780 coupled to microcontroller 720 by adata/address bus 782.

In some embodiments, the LPs 102 and 104 are configured to beimplantable in any chamber of the heart, namely either atrium (RA, LA)or either ventricle (RV, LV). Furthermore, for dual-chamberconfigurations, multiple LPs may be co-implanted (e.g., one in the RAand one in the RV, one in the RV and one in the coronary sinus proximatethe LV). Certain pacemaker parameters and functions depend on (orassume) knowledge of the chamber in which the pacemaker is implanted(and thus with which the LP is interacting; e.g., pacing and/orsensing). Some non-limiting examples include: sensing sensitivity, anevoked response algorithm, use of AF suppression in a local chamber,blanking & refractory periods, etc. Accordingly, each LP needs to knowan identity of the chamber in which the LP is implanted, and processesmay be implemented to automatically identify a local chamber associatedwith each LP.

Processes for chamber identification may also be applied to subcutaneouspacemakers, ICDs, with leads and the like. A device with one or moreimplanted leads, identification and/or confirmation of the chamber intowhich the lead was implanted could be useful in several pertinentscenarios. For example, for a DR or CRT device, automatic identificationand confirmation could mitigate against the possibility of the clinicianinadvertently placing the V lead into the A port of the implantablemedical device, and vice-versa. As another example, for an SR device,automatic identification of implanted chamber could enable the deviceand/or programmer to select and present the proper subset of pacingmodes (e.g., AAI or VVI), and for the IPG to utilize the proper set ofsettings and algorithms (e.g., V-AutoCapture vs ACap-Confirm, sensingsensitivities, etc.).

While many of the embodiments of the present technology described abovehave been described as being for use with LP type IMDs, embodiments ofthe present technology that are for use in reducing how often a firstreceiver of an IMD wakes up a second receiver of an IMD, in order toreduce power consumption, can also be used with other types of IMDsbesides an LP. Accordingly, unless specifically limited to use with anLP, the claims should not be limited to use with LP type IMDs. Forexample, embodiments of the present technology can also be used with asubcutaneous-ICD and/or a subcutaneous pacemaker, but are not limitedthereto.

It is to be understood that the subject matter described herein is notlimited in its application to the details of construction and thearrangement of components set forth in the description herein orillustrated in the drawings hereof. The subject matter described hereinis capable of other embodiments and of being practiced or of beingcarried out in various ways. Also, it is to be understood that thephraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having” and variations thereof herein ismeant to encompass the items listed thereafter and equivalents thereofas well as additional items. Further, it is noted that the term “basedon” as used herein, unless stated otherwise, should be interpreted asmeaning based at least in part on, meaning there can be one or moreadditional factors upon which a decision or the like is made. Forexample, if a decision is based on the results of a comparison, thatdecision can also be based on one or more other factors in addition tobeing based on results of the comparison.

Embodiments of the present technology have been described above with theaid of functional building blocks illustrating the performance ofspecified functions and relationships thereof. The boundaries of thesefunctional building blocks have often been defined herein for theconvenience of the description. Alternate boundaries can be defined solong as the specified functions and relationships thereof areappropriately performed. Any such alternate boundaries are thus withinthe scope and spirit of the claimed invention. For example, it would bepossible to combine or separate some of the steps shown in FIGS. 6A and6B. For another example, it is possible to change the boundaries of someof the dashed blocks shown in FIGS. 2 and 7 .

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the embodiments ofthe present technology without departing from its scope. While thedimensions, types of materials and coatings described herein areintended to define the parameters of the embodiments of the presenttechnology, they are by no means limiting and are exemplary embodiments.Many other embodiments will be apparent to those of skill in the artupon reviewing the above description. The scope of the embodiments ofthe present technology should, therefore, be determined with referenceto the appended claims, along with the full scope of equivalents towhich such claims are entitled. In the appended claims, the terms“including” and “in which” are used as the plain-English equivalents ofthe respective terms “comprising” and “wherein.” Moreover, in thefollowing claims, the terms “first,” “second,” and “third,” etc. areused merely as labels, and are not intended to impose numericalrequirements on their objects. Further, the limitations of the followingclaims are not written in means-plus-function format and are notintended to be interpreted based on 35 U.S.C. § 112(f), unless and untilsuch claim limitations expressly use the phrase “means for” followed bya statement of function void of further structure.

What is claimed is:
 1. A method for use with an implantable medicaldevice (IMD), the method comprising: during each message alert period ofa plurality of message alert periods during which a communicationcapability of the IMD is enabled, determining whether a valid message isdetected during the message alert period; temporarily disabling thecommunication capability of the IMD for a disable period, in response todetermining that no valid message was detected during a said messagealert period; and increasing a length of the disable period in responseto no valid message being detected during two consecutive said messagealert periods.
 2. The method of claim 1, wherein: the increasing thelength of the disable period, in response to no valid message beingdetected during two consecutive said message alert periods, comprisesincreasing the length of the disable period from a first number ofcardiac cycles to a second number of cardiac cycles; the first number isone or greater; and the second number is greater than the first number.3. The method of claim 1, wherein: the increasing the length of thedisable period, in response to no valid message being detected duringtwo consecutive said message alert periods, comprises increasing thelength of the disable period from a first length of time to a secondlength of time that is longer than the first length of time.
 4. Themethod of claim 1, further comprising: further increasing the length ofthe disable period in response to no valid message being detected duringthree consecutive message alert periods.
 5. The method of claim 1,wherein: the communication capability of the IMD, which is temporarilydisabled, comprises a communication capability related to at least oneof a receiver or a transmitter of the IMD.
 6. The method of claim 1,wherein: the IMD includes both a first receiver and a second receiver,wherein the first receiver is used to selectively wakeup the secondreceiver, and wherein the communication capability of the IMD, which istemporarily disabled, comprises a communication capability related tothe first receiver.
 7. The method of claim 1, wherein the IMD comprisesa first leadless pacemaker (LP1) that is configured to communicate witha second leadless pacemaker (LP2) so that the LP1 and the LP2 candeliver synchronized therapy.
 8. A method for use with an implantablemedical device (IMD), the method comprising: during each message alertperiod of a plurality of message alert periods during which acommunication capability of the IMD is enabled, determining whether avalid message is detected during the message alert period; andtemporarily disabling the communication capability of the IMD for adisable period, in response to determining that no valid message wasdetected during a said message alert period; wherein a length of thedisable period is dependent on an operational mode of the IMD, such thatthe length of the disable period when the IMD is operating in a firstoperational mode differs from the length of the disable period when theIMD is operating in a second operational mode.
 9. The method of claim 8,wherein: the first operational mode comprises a normal operational modeof the IMD; the second operational mode comprises a magnetic resonanceimaging (MRI) ready operational mode; and the length of the disableperiod when the IMD is operating in the MRI ready operational mode islonger than the disable period when the IMD is operating in the normaloperational mode.
 10. The method of claim 8, wherein: the length of thedisable period when the IMD is operating in the first operational modecomprises a first length of time or a first number of cardiac cycles;the length of the disable period when the IMD is operating in the secondoperational mode, which is greater than the length of the disable periodwhen the IMD is operating in the first operational mode, comprises asecond length of time or a second number of cardiac cycles; and thelength of the disable period when the IMD is operating in a thirdoperational mode, which is greater than the length of the disable periodwhen the IMD is operating in the second operational mode, comprises athird length of time or a third number of cardiac cycles.
 11. The methodof claim 10, wherein: the first operational mode comprises a normaloperational mode of the IMD; the second operational mode comprises amagnetic resonance imaging (MRI) ready operational mode; and the thirdoperational mode comprises a radio frequency (RF) ablation readyoperational mode.
 12. The method of claim 8, wherein: the communicationcapability of the IMD, which is temporarily disabled, comprises acommunication capability related to at least one of a receiver or atransmitter of the IMD.
 13. The method of claim 8, wherein: the IMDincludes both a first receiver and a second receiver, wherein the firstreceiver is used to selectively wakeup the second receiver, and whereinthe communication capability of the IMD, which is temporarily disabled,comprises a communication capability related to the first receiver. 14.The method of claim 8, wherein the IMD comprises a first leadlesspacemaker (LP1) that is configured to communicate with a second leadlesspacemaker (LP2) so that the LP1 and the LP2 can deliver synchronizedtherapy.
 15. A method for use with an implantable medical device (IMD)that is configured to perform pacing therapy, the method comprising:during each message alert period of a plurality of message alert periodsduring which a communication capability of the IMD is enabled,determining whether a valid message is detected during the message alertperiod; in response to determining that no valid message was detectedduring a said message alert period, temporarily disabling thecommunication capability of the IMD for a disable period and causing theIMD to enter a noise state during which a pacing mode of the IMD doesnot depend on communicating with another IMD; and following the IMDentering into the noise state, maintaining the IMD in the noise stateuntil a specified number of valid messages are received by the IMD. 16.The method of claim 15, further comprising: causing the IMD to exit thenoise state, in response to determining that the specified number ofvalid message were received by the IMD while the IMD was in the noisestate.
 17. The method of claim 15, further comprising: pacing inaccordance with one of a DDD, DDI, VDD, VDI, or DOO mode when the IMD isnot in the noise state; and pacing in accordance with one of a VVI orVOO mode when the IMD is in the noise state.
 18. The method of claim 15,wherein: the communication capability of the IMD, which is temporarilydisabled, comprises a communication capability related to at least oneof a receiver or a transmitter of the IMD.
 19. The method of claim 15,wherein: the IMD includes both a first receiver and a second receiver,wherein the first receiver is used to selectively wakeup the secondreceiver, and wherein the communication capability of the IMD, which istemporarily disabled, comprises a communication capability related tothe first receiver.
 20. The method of claim 15, wherein the IMDcomprises a first leadless pacemaker (LP1) that is configured tocommunicate with a second leadless pacemaker (LP2) so that the LP1 andthe LP2 can deliver synchronized therapy, and wherein the other IMDcomprises the LP2.